This invention relates to diaphragm pumps and, more particularly, is concerned with an arrangement permitting variable delivery by limiting the pressure in the flow channels of such pumps.
Numerous designs of diaphragm pumps are available. For example, British Patent Specification No. 1,400,150 describes and claims a diaphragm pump having a tubular body, a tubular diaphragm received by the tubular body and defining with it a pressure chamber, and a piston and cylinder arrangement in communication with the pressure chamber. The piston is reciprocable in the cylinder, and one way valves adjacent the respective ends of the diaphragm serve to control flow of fluid through the pump's flow channel. Liquid is displaced between the pressure chamber and the cylinder when the pump is in operation, this displacement causing the cross-sectional area of the tubular diaphragm to vary thereby varying the volume and the pressure within the diaphragm to cause displacement of liquid therethrough. Such a pump is able to pump liquids such as water at relatively high pressures such as, for example, 5000 pounds per square inch (350 kg/cm.sup.2).
The present invention is concerned with a pump which functions in a manner analogous to that described in British Patent Specification No. 1,400,150. The invention aims to obviate or at least to ameliorate a disadvantage associated with pumps of this sort, namely that the pressure in the flow channel of the pump may rise to unacceptably high levels and that delivery from the pump is not easy to control.